Pumps, such as high pressure pumps, may be used in high pressure applications and may be close coupled or belt driven. Each pump includes a manifold that may be machined from a solid billet of titanium so as to be resistant to corrosion, for example from seawater. Because the manifolds are machined and not cast, voids or casting defects are avoided. The pumps include nylon face valves and titanium backing rings for quiet operation and corrosion resistance, and inlet and discharge valve assemblies that are interchangeable for maintenance purposes.